1. Field of the Invention
The present invention relates generally to fluid filled vibration damping devices exhibiting damping effect on the basis of flows of the non-compressible fluid sealed therein, and more particularly to a fluid filled vibration damping device of novel construction, which may be usable as an engine mount or other mounts for use in automotive vehicles.
2. Description of the Related Art
A fluid filled vibration damping device is known as one type of a vibration-damping coupling or mount adapted to be installed between two members of a vibration systems so as to elastically connect or support the two members in a vibration-damping fashion. Citation 1 shows an example of such a fluid filled vibration-damping device, which includes: a rubber elastic body elastically connecting a first and second mounting member fixable to one and the other member mutually connected in a vibration damping fashion, respectively; a pressure receiving chamber partially defined by the rubber elastic body and filled with a non compressible fluid; an equilibrium chamber partially defined by a flexible rubber layer and filled with the non-compressible fluid; and an orifice passage for permitting a fluid communication between the pressure-receiving chamber and the equilibrium chamber. Upon application of a vibrational load between the first and second mounting members, the fluid is forced to flow through the orifice passage between the pressure receiving chamber and the equilibrium chamber, so that the fluid filled vibration damping device can exhibit damping effect on the basis of resonance or flows of the fluid flowing through the orifice passage. In the fluid filled vibration damping device of this structure, the pressure receiving chamber and the equilibrium chamber are disposed on the opposite sides of the elastic body, making it possible to decrease a dimension of the device in the vertical or height direction. For the above-described advantage, the conventional fluid filled vibration damping device may be effectively usable as an automotive engine mount that is prone to be requested to be installed in a limited space.
[Citation]
JP-A-2001-59540
In the conventional vibration damping device, as indicated in Citation 1, the first mounting member is bonded to a central portion of the elastic body, and the second mounting member is bonded to an outer circumferential portion of the elastic body, while the flexible rubber layer is disposed surrounding and covering an outside of the rubber elastic body. The flexible rubber layer is bonded at its central portion to the first mounting member, and at its outer peripheral portion to the second mounting member. Typically, the elastic body and the flexible rubber layer are formed separately, since it is difficult to form the elastic body and the flexible rubber layer integrally due to their different requested characteristics, limitations comes from mold structures, or the like. For this reason, the first mounting member is composed of an elastic-body-side central member and a rubber-layer-side central member, and the elastic body and the flexible rubber layer are formed separately such that the elastic body is bonded at its central portion to the elastic-body-side central member, while the flexible rubber layer is bonded at its central portion to the rubber-layer-side central member. The elastic-body-side central member and the rubber-layer-side central member are superposed on each other and connected together by means of a connecting bolt, thereby providing the first mounting member.
However, the conventional fluid-filled vibration damping device of the aforesaid structure has still suffered from the following problems (1)–(3) upon fastening the two separate members (i.e., the elastic-body-side central member and the rubber-layer-side central member) together by means of the connecting bolt to provide the first mounting member.
(1) One problem is a difficulty in producing a reaction force against a tightening torque from the connecting bolt. That is, since the elastic-body-side central member is covered by the rubber-layer-side central member, it is impossible to directly hold the elastic-body-side central member in order to produce the reaction force against the tightening torque from the connecting bolt.
(2) Another problem is a low degree of freedom in designing a mounting portion of the first mounting member, which portion is utilized to fix the first mounting member to the one of the two members connected together in a vibration damping fashion. Namely, the connecting bolt is situated on a central portion of a surface of the rubber-layer-side central member, making it difficult to integrally form the mounting portion of desired configuration on the rubber-layer-side central member in view of a space. To form such a mounting portion, unavoidable is an enlargement of the rubber-layer-side central member. The citation 1 discloses a conventional structure in which the mounting portion is formed by utilizing the connecting bolt. However, it is apparent that the conventional structure is not adapted sufficiently for a variety of structures or shapes of members to which the first mounting member is fixed.
(3) A further problem is that when fastening the elastic-body-side central member and the rubber-layer-side central member together by means of the connecting bolt, mutually aligned bolt holes of these members are prone to be dislocated from each other during insertion the connecting bolt into these bolt holes, making it cumbersome to assemble these members. Namely, the elastic-body-side central member and the rubber-layer-side central member are prone to be dislocated from each other at their abutting surfaces, making it difficult to align the bolt holes of these members to each other, and to hold these member in a mutually aligned state.
It may be proposed to fasten the elastic-body-side central member and the rubber-layer-side central member together by caulking or other appropriate methods, without using the mounting bolt. However, a caulking operation needs a specific device, undesirably pushing a manufacturing cost up. In the case where the elastic-body-side central member and the rubber-layer-side central member are formed of aluminum alloy, the caulking operation may not be employable in view of insufficient strength and durability of the members.